\linespread{1.3}%1.3倍行距
\usepackage{tabularx}
\newcolumntype{Z}{>{\centering\arraybackslash}X}%设置 Z 居中的效果
\setlist[enumerate]{leftmargin=0pt}%设置列表环境左边的间距
\newcommand{\ee}{\mathrm{e}}%常见符号
\newcommand{\dd}{\,\mathrm{d}}
\newcommand{\ii}{\mathrm{i}}
\newcommand{\Ln}{\mathrm{Ln\,}}
\newcommand{\Res}{\,\mathrm{Res}}
\newcommand{\LL}{\mathscr{L}}
\newcommand{\EE}{\mathbb{E}\,}
\renewcommand{\leq}{\leqslant}
\renewcommand{\geq}{\geqslant}
\newcommand{\Cov}{\mathrm{Cov}}

%\everymath{\displaystyle}

%排选择题
\newcommand{\fourch}[4]{\\\begin{tabular}{*{4}{@{}p{4cm}}}(A)~#1 & (B)~#2 & (C)~#3 & (D)~#4\end{tabular}} % 一行
\newcommand{\twoch}[4]{\\\begin{tabular}{*{2}{@{}p{8cm}}}(A)~#1 & (B)~#2\end{tabular}\\\begin{tabular}{*{2}{@{}p{8cm}}}(C)~#3 & (D)~#4\end{tabular}}  %两行
\newcommand{\onech}[4]{\\(A)~#1 \\ (B)~#2 \\ (C)~#3 \\ (D)~#4}  % 四行